AS1261: the NATINST-AS-AS network

AS1261 is an internet Autonomous System operated by NATINST-AS-AS (the United States). Here is what that means and why this number may show up when you investigate a connection on your network.

What is AS1261?

An Autonomous System (ASN) is a block of networks under a single control with its own routing policy on the internet. The number AS1261 was assigned to NATINST-AS-AS by an RIR (regional internet registry). All traffic entering or leaving that network is announced under this number.

Reach on the internet

AS1261 currently announces 7 IPv4 block(s), totaling about 3.3 thousand addresses (3,328 in all), registered in the United States. Services from NATINST-AS-AS are reached through these addresses.

What it means to see AS1261 on your network

When you investigate where a connection from your computer or phone comes from (or goes to), you may find AS1261. That means the other end sits on the NATINST-AS-AS network (the United States). It can be legitimate — a cloud service, an ISP, a CDN — or an unexpected connection worth checking.

How to see every connection and network your devices reach

Tracing one connection's ASN at a time is tedious. Sentinela, by PC Monitor, maps the devices on your network, shows what is exposed to the internet and helps flag suspicious connections and devices — running on your Windows. Meet Sentinela.